1. Field of the Invention
The present invention relates to a technique for detecting the chip temperature of a power transistor, which drives a load such as an inductive load or a resistive load, quickly, at a low cost, and at high accuracy, so that it enables the entire system to operate safely.
2. Description of the Related Art
From the past, various protective circuits have been indispensable for the proper utilization of a power transistor, such as circuits for protection from excess electrical current and for protection from excess load (excess temperature) and the like. It is per se known to utilize a mirror transistor in which flows an electrical current which is proportional to the main electrical current as a current detection means for protection from excess electrical current, and it is per se known to use a chip temperature detection means for protection from excess load. As one example of a prior art chip temperature detection means, there is a per se known method of forming a diode in a polysilicon thin film upon the surface of the power transistor, and of detecting the temperature by taking advantage of the temperature dependence of the bias voltage when a fixed electric current flows in the forward direction through said polysilicon diode. This method has the beneficial point of being easy to apply, since such a polysilicon diode is perfectly separated from the power transistor by an dielectric material., and accordingly they do not mutually interfere with one another.